A chlorosulphonated polyethylene obtained by chlorinating and chlorosulphonating a high density polyethylene has excellent ozone resistance, weather-proof resistance, heat resistance and, oil resistance and chemical resistance, and due to such excellent properties, is used as wires, hoses, escalator handrails, and the like. However, because of poor low temperature property, the chlorosulphonated polyethylene is not used in belts for automobiles, boots, and the like. On the other hand, a chlorosulphonated ethylene-α-olefin copolymer disclosed in JP-B-5-17243 has excellent low temperature property as compared with a chlorosulphonated polyethylene using a high density polyethylene as a raw material, and therefore is applied to uses requiring low temperature property, to which the conventional chlorosulphonated polyethylene has been difficult to apply.
Patent publications (foe example, JP-A-9-176394, JP-A-8-67712 and JP-A-61-145204) relating to improvement of low temperature property of a chlorosulphonated ethylene-α-olefin copolymer are reported for expansion of application of the same to uses requiring low temperature property.
However, there is no report of a chlorosulphonated ethylene-α-olefin copolymer having a glass transition temperature of −50° C. or lower so as to further improve the low temperature property.